Ion-exchange resins may be poisoned by the adsorption of substances that are either very difficult to remove or are very easily removed from the polymeric structure of the resin. A guard chamber containing activated carbon has been employed for the protection of an anion exchange resin column used in the purification of uranium values. This system operates in a pH range of 5-10. See, U.S. Pat. No. 4,296,075.
Cation and anion exchange resin pairs (or systems) are used extensively in the purification of sweetener solutions, for example, corn syrups, cane syrups, beet syrups and in other sweetener applications. These ion-exchange resin systems are especially useful in purifying dextrose syrups for the production of high fructose corn syrups (HFCS). These resins are employed for the removal of ash, specifically conductometric ash as measured by the beverage industry. A key cause of unwanted syrup conductance is the presence of salts resulting from neutralization reactions during the processing of the syrup. While the cation and anion exchange resins are effective in removing these salts, other components present in crude sweetener solution also contribute to this undesirable syrup conductivity. These other components are generally weak organic acids, generated by the breakdown of starches or proteins. These acids include citric, glutamic, lactic, tartaric and others. Generally, the specific acids are not identified. Rather, the mixture of acids in the syrup are termed "titratable acidity". These weak organic acids are removed by the anion exchange resin as negatively charged organic anions. However, due to the low charge density of some of these acids, they are easily displaced from the anion exchange resin. This results in an early rollover of the organic acids from the anion exchange resin causing an unacceptable rise in syrup conductance. This rollover or bleed of organic acids into the syrup triggers a need for regeneration of the anion exchange resin before it has been fully utilized. Others of these acids will not be readily displaced and will occupy exchange sites which are then unavailable to the inorganic ash constituents thereby also shortening the useful resin cycle. Such exchange resin system downtime is wasteful both from a processing (time) standpoint and an economic standpoint.
It has been discovered, that the ion-exchange system downtime can be reduced, and hence, overall process efficiency increased, if the weak undissociated acids in the sweetener syrup are removed before they enter the anion exchange resin. These acids are adsorbed on a properly positioned microporus adsorbent within the ion exchange resin system.